[jewel]

In this particular case, the HTML5 <input type=color> works great. (Not on IE yet, but there is a polyfill.)

In the long run, shadow DOM should make it easier to make framework agnostic widgets.

[jawngee]

Doesn't work on Safari either.

http://caniuse.com/#feat=input-color

[look_lookatme]

Doesn't support opacity, but this one does now.